I. Field
The present invention relates generally to communication, and more specifically to cell measurements in asynchronous communication networks.
II. Background
Wireless communication networks are widely deployed to provide various communication services such as voice, packet data, and so on. These wireless networks may be capable of supporting multiple users by sharing the available system resources. Examples of such wireless networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, and Frequency Division Multiple Access (FDMA) networks. These wireless networks may also utilize various radio access technologies (RATs) such as Wideband-CDMA (W-CDMA), cdma2000, Global System for Mobile Communications (GSM), and so on, all of which are well known in the art.
A multi-mode terminal is capable of communicating with multiple wireless networks, such as a GSM network and a W-CDMA network. The multi-mode terminal typically communicates with a serving cell in only one wireless network at any given moment but periodically makes measurements for cells in the other wireless network. The cell measurements allow the terminal to ascertain whether any cell in the other wireless network is better than the current serving cell. This may be the case, for example, if the terminal is mobile and moves to a different coverage area. If a better cell in the other wireless network is found, as indicated by the cell measurements, then the terminal may attempt to switch to the other wireless network and receive service from the better cell.
Each cell in a GSM network periodically transmits a synchronization burst that allows the terminals to make measurements for that cell. Each GSM cell transmits its synchronization burst at specific time instances determined by the timing of that cell. The GSM and W-CDMA networks may operate asynchronously so that the timing of the cells in the GSM network cannot be ascertained based on the timing of the cells in the W-CDMA network, and vice versa. Furthermore, the cells in each network may operate asynchronously of one another. The asynchronous operation at the network and cell levels complicates cell measurement.
There is therefore a need in the art for techniques to efficiently make cell measurements in asynchronous communication networks.